Structure of fuel injector adjustable in fuel jet characteristic

Abstract

A fuel injector is provided which has an improved structure capable of adjusting fuel jet characteristics such as the quantity of fuel to be injected to an engine and a fuel injection time lag after the fuel injector is assembled. The fuel injector includes an air gap adjusting screw and a spring pressure adjusting screw. The air gap adjusting screw serves to change an air gap between a stator and an armature of a solenoid valve to adjust the quantity of fuel to a target one. The spring pressure adjusting screw serves to change a spring pressure urging a valve in a spray hole-closing direction to regulate a spray hole open duration, thereby adjusting the fuel injection time lag or the quantity of fuel.

What is claimed is:  
     
       1. A fuel injector comprising: 
       a nozzle having formed therein a spray hole from which fuel is sprayed;  
       a nozzle valve selectively opening and closing the spray hole;  
       an injector body supporting therein said nozzle valve slidably, said injector body having formed therein a fuel sump supplied with the fuel from an inlet formed in said injector body to produce fuel pressure urging said nozzle valve in a spray hole-opening direction, a pressure chamber supplied with the fuel from the inlet to produce fuel pressure urging said nozzle valve in a spray hole-closing direction, and a valve hole establishing fluid communication between the pressure chamber and a drain port formed in said injector body;  
       a control valve selectively opening and closing the valve hole formed in said injector body;  
       a first urging mechanism urging said control valve in a valve hole-closing direction for closing the valve hole to block the fluid communication between the pressure chamber and the drain port;  
       a control valve moving mechanism made up of a stationary portion and a movable portion, the stationary portion including a stator and a coil, the movable portion including an armature which is connected fixedly to said control valve and spaced from the stator through a given air gap, the coil being energized electrically to produce an attractive force through the stator for attracting the armature to move said control valve in a valve hole-opening direction, thereby opening the valve hole to establish the fluid communication between the pressure chamber and the drain port;  
       a second urging mechanism urging the stationary portion of said control valve moving mechanism in a first direction identical with the valve hole-opening direction; and  
       an air gap adjusting member disposed around the stationary portion of said control valve moving mechanism in engagement with said injector body so as to urge the stationary portion of said control valve moving mechanism in a second direction opposite the first direction against an urging pressure produced by said second urging mechanism to keep the air gap between the stator and the armature, said air gap adjusting member being designed to be movable selectively in said first direction and second direction for changing the air gap.  
     
     
       2. A fuel injector as set forth in  claim 1 , wherein said air gap adjusting mechanism is connected to said injector body in a screw fashion. 
     
     
       3. A fuel injector as set forth in  claim 2 , wherein said air gap adjusting mechanism has formed therein an internal thread engaging an outer thread formed on an end portion of said injector body and forms a sliding pair with said control pair moving mechanism. 
     
     
       4. A fuel injector as set forth in  claim 1 , wherein said air gap adjusting mechanism is made of a hollow member fitted on said injector body. 
     
     
       5. A fuel injector as set forth in  claim 1 , wherein said second urging mechanism is implemented by a disc spring disposed within said injector body. 
     
     
       6. A fuel injector comprising: 
       a nozzle having formed therein a spray hole from which fuel is sprayed;  
       a nozzle valve selectively opening and closing the spray hole;  
       an injector body supporting therein said nozzle valve slidably, said injector body having formed therein a fuel sump supplied with the fuel from an inlet formed in said injector body to produce fuel pressure urging said nozzle valve in a spray hole-opening direction, a pressure chamber supplied with the fuel from the inlet to produce fuel pressure urging said nozzle valve in a spray hole-closing direction, and a valve hole for establishing fluid communication between the pressure chamber and a drain port formed in said injector body;  
       a valve chamber formed in said injector body downstream of the valve hole;  
       a control valve movable within said valve chamber to selectively open and close the valve hole formed in said injector body, when leaving the valve hole, said control valve defining in said valve chamber a first drain passage communicating with the pressure chamber through the valve hole;  
       an urging mechanism disposed within an urging mechanism mount chamber formed in said injector body leading to the first drain passage, said urging mechanism working to produce an urging pressure which urges said control valve in a valve hole-closing direction for closing the valve hole to block the fluid communication between the pressure chamber and the valve chamber;  
       a control valve moving mechanism made up of a stationary portion and a movable portion, the stationary portion including a stator and a coil, the movable portion including an armature which is connected fixedly to said control valve, the coil being energized electrically to produce an attractive force through the stator for attracting the armature to move said control valve in a valve hole-opening direction against the urging pressure produced by said urging mechanism, thereby opening the valve hole to establish the fluid communication between the pressure chamber and the first drain passage; and  
       an urging pressure adjusting mechanism disposed within said injector body in contact with said urging mechanism, said urging pressure adjusting mechanism being so designed as to be movable in engagement with an inner wall of the urging mechanism mount chamber for changing the urging pressure produced by said urging mechanism, said urging pressure adjusting mechanism having formed therein a second drain passage communicating between the first drain passage and the drain port through the urging mechanism mount chamber.  
     
     
       7. A fuel injector as set forth in  claim 6 , wherein said urging pressure adjusting mechanism engages the inner wall of the urging mechanism mount chamber in a screw fashion. 
     
     
       8. A fuel injector as set forth in  claim 6 , wherein said urging pressure adjusting mechanism is press-fitted within the urging mechanism mount chamber. 
     
     
       9. A fuel injector as set forth in  claim 6 , further comprising: 
       a second urging mechanism urging the stationary portion of said control valve moving mechanism in a first direction identical with the valve hole-opening direction; and  
       an air gap adjusting member disposed around the stationary portion of said control valve moving mechanism in engagement with said injector body so as to urge the stationary portion of said control valve moving mechanism in a second direction opposite the first direction against an urging pressure produced by said second urging mechanism to keep an air gap between the stator and the armature, said air gap adjusting member being designed to be movable selectively in said first direction and second direction for changing the air gap.  
     
     
       10. A fuel injector as set forth in  claim 9 , wherein said air gap adjusting mechanism is connected to said injector body in a screw fashion. 
     
     
       11. A fuel injector as set forth in  claim 10 , wherein said air gap adjusting mechanism has formed therein an internal thread engaging an outer thread formed on an end portion of said injector body and forms a sliding pair with said control pair moving mechanism. 
     
     
       12. A fuel injector as set forth in  claim 9 , wherein said air gap adjusting mechanism is made of a hollow member fitted on said injector body. 
     
     
       13. A fuel injector as set forth in  claim 9 , wherein said second urging mechanism is implemented by a disc spring disposed within said injector body. 
     
     
       14. A method of adjusting a fuel injection characteristic of a fuel injector which is designed to inject fuel into an engine and which includes: 
       (a) a nozzle having formed therein a spray hole from which fuel is sprayed;  
       (b) a nozzle valve selectively opening and closing the spray hole;  
       (c) an injector body supporting therein said nozzle valve slidably, said injector body having formed therein a fuel sump supplied with the fuel from an inlet formed in said injector body to produce fuel pressure urging said nozzle valve in a spray hole-opening direction, a pressure chamber supplied with the fuel from the inlet to produce fuel pressure urging said nozzle valve in a spray hole-closing direction, and a valve hole establishing fluid communication between the pressure chamber and a drain port formed in said injector body;  
       (d) a control valve selectively opening and closing the valve hole formed in said injector body; and  
       (e) a control valve moving mechanism made up of a stationary portion and a movable portion, the stationary portion including a stator and a coil wound around the stator, the movable portion including an armature which is connected fixedly to said control valve and spaced from the stator through a given air gap, the coil being energized electrically to produce an attractive force through the stator for attracting the armature to move said control valve in a valve hole-opening direction, thereby opening the valve hole to establish the fluid communication between the pressure chamber and the drain port so that the fuel pressure in the pressure chamber is decreased to move said nozzle valve so as to open the spray hole,  
       said method comprising the steps of:  
       supplying a test liquid to said fuel injector from the inlet at a given pressure level higher than half a maximum pressure of the fuel which is supplied to the fuel sump and the pressure chamber when the fuel injector is actually used to inject the fuel into the engine;  
       applying a drive pulse signal to the coil of said control valve moving mechanism to energize the coil for spraying the test liquid from the spray hole; and  
       changing the air gap between the stator and the armature to adjust a quantity of the test liquid sprayed from the spray hole to a target one.  
     
     
       15. A method as set forth in  claim 14 , wherein said fuel injector further comprises a first urging mechanism urging said control valve in a valve hole-closing direction for closing the valve hole to block the fluid communication between the pressure chamber and the drain port; a second urging mechanism urging the stationary portion of said control valve moving mechanism in a first direction identical with the valve hole-opening direction, and an air gap adjusting member disposed around the stationary portion of said control valve moving mechanism in engagement with said injector body so as to urge the stationary portion of said control valve moving mechanism in a second direction opposite the first direction against an urging pressure produced by said second urging mechanism to keep the air gap between the stator and the armature, said air gap adjusting member being designed to be movable selectively in said first direction and second direction for changing the air gap, and wherein said air gap changing step moves said air gap adjusting mechanism to change the air gap between the stator and the armature to adjust the quantity of the test liquid sprayed from the spray hole to the target one. 
     
     
       16. A method as set forth in  claim 14 , wherein said drive pulse applying step applies a first drive pulse signal and a second drive pulse signal having a width different from that of the first drive pulse signal in sequence to the coil of said control valve moving mechanism to energize the coil during said air gap changing step. 
     
     
       17. A method as set forth in  claim 16 , wherein the width of the first drive pulse signal is longer than that required to move said nozzle valve until a maximum rate of a jet of the test liquid from the spray hole is reached. 
     
     
       18. A method as set forth in  claim 16 , wherein if target quantities of the test liquid sprayed from the spray hole when the first and second drive pulse signals are applied to the coil of said control valve moving mechanism are defined as a first and a second target value, respectively, a difference between a quantity of the test liquid sprayed from the spray hole when the first drive pulse signal is applied to the coil and the first target value is defined as δ 1 , a difference between a quantity of the test liquid sprayed from the spray hole when the second drive pulse signal is applied to the coil and the second target value is defined as β 2 , said air gap changing step changes the air gap so as to meet at least one of a condition of δ 1   2 +δ 2   2 ≦K 1  and a condition of δ 1 ×δ 2 <0, δ 1 ≦K 2 , and δ 2 ≦K 3  where K 1 , K 2 , and K 3  are preselected target values, respectively. 
     
     
       19. A method of adjusting a fuel injection characteristic of a fuel injector which is designed to inject fuel into an engine and which includes: 
       (f) a nozzle having formed therein a spray hole from which fuel is sprayed;  
       (g) a nozzle valve selectively opening and closing the spray hole;  
       (h) an injector body supporting therein said nozzle valve slidably, said injector body having formed therein a fuel sump supplied with the fuel from an inlet formed in said injector body to produce fuel pressure urging said nozzle valve in a spray hole-opening direction, a pressure chamber supplied with the fuel from the inlet to produce fuel pressure urging said nozzle valve in a spray hole-closing direction, and a valve hole establishing fluid communication between the pressure chamber and a drain port formed in said injector body;  
       (i) a control valve selectively opening and closing the valve hole formed in said injector body;  
       (j) an urging mechanism disposed within an urging mechanism mount chamber formed in said injector body, said urging mechanism working to produce an urging pressure which urges said control valve in a valve hole-closing direction for closing the valve hole to block the fluid communication between the pressure chamber and the drain port; and  
       (k) a control valve moving mechanism made up of a stationary portion and a movable portion, the stationary portion including a stator and a coil wound around the stator, the movable portion including an armature which is connected fixedly to said control valve, the coil being energized electrically to produce an attractive force through the stator for attracting the armature to move said control valve in a valve hole-opening direction, thereby opening the valve hole to establish the fluid communication between the pressure chamber and the drain port so that the fuel pressure in the pressure chamber is decreased to move said nozzle valve so as to open the spray hole,  
       said method comprising the steps of:  
       supplying a test liquid to said fuel injector from the inlet at a given pressure level higher than half a maximum pressure of the fuel which is supplied to the pressure chamber when the fuel injector is actually used to inject the fuel into the engine;  
       applying a drive pulse signal to the coil of said control valve moving mechanism to energize the coil for spraying the test liquid from the spray hole; and  
       changing the urging pressure produced by said urging mechanism to adjust a quantity of the test liquid sprayed from the spray hole to a target one.  
     
     
       20. A method as set forth in  claim 19 , further comprising an urging pressure adjusting mechanism disposed within said injector body in contact with said urging mechanism, said urging pressure adjusting mechanism being so designed as to be movable in engagement with an inner wall of the urging mechanism mount chamber for changing the urging pressure produced by said urging mechanism, said urging pressure adjusting mechanism having formed therein a second drain passage communicating between a first drain passage communicating with the pressure chamber through the valve hole and the drain port through the urging mechanism mount chamber, and wherein said urging pressure changing step moves said urging pressure adjusting mechanism to shift said urging mechanism for adjusting the quantity of the test liquid sprayed from the spray hole to the target one. 
     
     
       21. A method as set forth in  claim 20 , wherein said drive pulse applying step applies a first drive pulse signal and a second drive pulse signal having a width different from that of the first drive pulse signal in sequence to the coil of said control valve moving mechanism to energize the coil during said air gap changing step. 
     
     
       22. A method as set forth in  claim 21 , wherein the width of the first drive pulse signal is longer than that required to move said nozzle valve until a maximum rate of a jet of the test liquid from the spray hole is reached. 
     
     
       23. A method as set forth in  claim 21 , wherein if target quantities of the test liquid sprayed from the spray hole when the first and second drive pulse signals are applied to the coil of said control valve moving mechanism are defined as a first and a second target value, respectively, a difference between a quantity of the test liquid sprayed from the spray hole when the first drive pulse signal is applied to the coil and the first target value is defined as δ 1 , a difference between a quantity of the test liquid sprayed from the spray hole when the second drive pulse signal is applied to the coil and the second target value is defined as δ 2 , said air gap changing step changes the air gap so as to meet at least one of a condition of δ 1   2 +δ 2   2 ≦K 1  and a condition of δ 1 ×δ 2 ≦0, δ 1 ≦K 2 , and δ 2 ≦K 3  where K 1 , K 2 , and K 3  are preselected target values, respectively. 
     
     
       24. A method of adjusting a fuel injection characteristic of a fuel injector which is designed to inject fuel into an engine and which includes: 
       (l) a nozzle having formed therein a spray hole from which fuel is sprayed;  
       (m) a nozzle valve selectively opening and closing the spray hole;  
       (n) an injector body supporting therein said nozzle valve slidably, said injector body having formed therein a fuel sump supplied with the fuel from an inlet formed in said injector body to produce fuel pressure urging said nozzle valve in a spray hole-opening direction, a pressure chamber supplied with the fuel from the inlet to produce fuel pressure urging said nozzle valve in a spray hole-closing direction, and a valve hole establishing fluid communication between the pressure chamber and a drain port formed in said injector body;  
       (o) a control valve selectively opening and closing the valve hole formed in said injector body;  
       (p) an urging mechanism disposed within an urging mechanism mount chamber formed in said injector body, said urging mechanism working to produce an urging pressure which urges said control valve in a valve hole-closing direction for closing the valve hole to block the fluid communication between the pressure chamber and the drain port; and  
       (q) a control valve moving mechanism made up of a stationary portion and a movable portion, the stationary portion including a stator and a coil wound around the stator, the movable portion including an armature which is connected fixedly to said control valve and spaced from the stator through an air gap, the coil being energized electrically to produce an attractive force through the stator for attracting the armature to move said control valve in a valve hole-opening direction, thereby opening the valve hole to establish the fluid communication between the pressure chamber and the drain port so that the fuel pressure in the pressure chamber is decreased to move said nozzle valve so as to open the spray hole,  
       said method comprising:  
       a first step of changing the urging pressure produced by said urging mechanism while supplying a test liquid to said fuel injector from the inlet and applying a drive pulse signal to the coil of said control valve moving mechanism to energize the coil for spraying the test liquid from the spray hole so as to have an injection lag time fall in a target range; and  
       a second step of changing the air gap between the stator and the armature while supplying a test liquid to said fuel injector from the inlet and applying a drive pulse signal to the coil of said control valve moving mechanism to energize the coil for spraying the test liquid from the spray hole so as to have a quantity of the test liquid sprayed from the spray hole fall in a target range.  
     
     
       25. A method as set forth in  claim 24 , wherein the test liquid is supplied at a given pressure level lower than half a maximum pressure of the fuel which is supplied to the pressure chamber when the fuel injector is actually used to inject the fuel into the engine in the first step. 
     
     
       26. A method as set forth in  claim 24 , wherein the test liquid is supplied at a given pressure level higher than half a maximum pressure of the fuel which is supplied to the pressure chamber when the fuel injector is actually used to inject the fuel into the engine in the second step. 
     
     
       27. A method as set forth in  claim 24 , wherein the second step applies first and second drive pulse signal having different widths alternately to the coil of said control valve moving mechanism. 
     
     
       28. A method as set forth in  claim 27 , wherein in the second step, at least one of the first and second drive pulse signals has the width greater than a width required for moving said nozzle valve up to a level where a maximum rate of spraying of the test liquid from the spray hole is reached. 
     
     
       29. A method as set forth in  claim 27 , wherein if target quantities of the test liquid sprayed from the spray hole when the first and second drive pulse signals are applied to the coil of said control valve moving mechanism are defined as a first and a second target value, respectively, a difference between a quantity of the test liquid sprayed from the spray hole when the first drive pulse signal is applied to the coil and the first target value is defined as δ 1 , a difference between a quantity of the test liquid sprayed from the spray hole when the second drive pulse signal is applied to the coil and the second target value is defined as δ 2 , said air gap changing step changes the air gap so as to meet at least one of a condition of δ 1   2 +δ 2   2 ≦K 1  and a condition of δ 1 ×δ 2 <0, δ 1 ≦K 2 , and δ 2 ≦K 3  where K 1 , K 2 , and K 3  are preselected target values, respectively.